1. Field of the Invention
The present invention relates to methods for making foam structures, and more specifically, it relates to method for making fine-cell foam-structures of metals or ceramics by coating a carbon substrate formed by the sol-gel process.
2. Description of Related Art
Fine-cell structures of metal or ceramic are desirable for many uses. Foams having cell sizes that are less than 20 microns in diameter are needed for retention of liquids and compounds. These small cell foams slow the leakage of such liquids from the foams to reduce immediate spills. The small cell sizes have utility, e.g., in applications such as catalysis, fuel cells, hydrogen storage and sensors. Currently, metal and ceramic foams are formed by utilizing a foaming step. The resulting foam has a cell structure that is uncontrolled. The following patents are exemplary. U.S. Pat. No. 6,998,535, titled: “Metal foam casting apparatus and method” is directed to a method for casting articles from metal foam includes a molten metal bath and a foam forming means. The foam is drawn into a ladle, within a heated chamber, which transports a foam sample to a mold. The ladle deposits the foam sample into the mold and the mold is closed. Once cooled and hardened the formed article is removed. The system of the invention comprises a molten metal bath, a heated foam collecting chamber, a ladle for drawing a sample of the foam and for transporting the sample to a mold. The present invention provides an apparatus for carrying out. U.S. Pat. No. 6,915,834, titled: “Process for producing metal foam and metal body produced using this process” relates to a process for producing metal foam and to a metal body produced using this process. The object is achieved by a process for producing metal foam by adding a blowing agent to a metal melt, wherein the metal melt is introduced into the die cavity of a metal die-casting machine and is foamed using a blowing agent which releases gases and is solid at room temperature. U.S. Pat. No. 6,932,925, titled: “Method of manufacturing a super-lightweight ceramic foam” is directed to a lightweight ceramic foam with a cellular structure effectively reinforced by ceramic short fibers, which has a density of 0.2 g/cm.sup.3 or less and a sufficient strength. The ceramic foam is prepared by evenly dispersing ceramic short fibers throughout a nonaqueous solvent through the use of the reactivity of metal alkoxide with the surface of the ceramic short fibers, adding into the nonaqueous solvent an aqueous slurry containing ceramic powder dispersed therein, allowing the evenly dispersed ceramic fibers to move into an aqueous phase separately from a nonaqueous solvent phase so as to obtain an aqueous slurry containing the ceramic fibers evenly dispersed therein, and foaming and firing the aqueous slurry. Methods for forming metal or ceramic foams having specified cell sizes are desirable for a variety of applications. The present invention provides such methods.